Wave detecting system



Patented Apr. 9, 1935 PATENT OFFICE WAVE DETECTING SYSTEM Russell S. Ohl, Little Silver, N. J., assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Original application September 1'7, 1931, Serial No. 563,265. Patent No. 1,950,123, March 6,,

1934. Divided and this application October 10,

1933, Serial No. 692,919

10 Claims. (Cl. 250-27) This invention relates to wave detectors and particularly to systems having increased sensi- In a highly sensitive detecting system it is,

necessaryffor the detecting elementto respond to a very slight change in the intensity of the received wave and to produce a resultant change in the detected current which is proportionately much greater than the change in the received wave. The damping introduced into any tuned circuit or, filter involved in the action of the detector should be of such magnitude as to permit the, required rapidity of response.

'In accordance with the invention one or more space discharge devices or. vacuum tubes are employed in cascade arrangement, coupled by resonant circuits tuned to a suitably high frequency. Each of the space discharge devices is normally, polarized by a potential at least sufiicient to block its own space discharge. The blocking renders the system insensitive to waves of weak intensity. but this condition may be overcome by initial amplification whereby waves of a preassigned strength are amplified to thepoint at which the blocking is overcome.

' Each of the space discharge devices when suitcircuit for operating a relayin accordance with the invention;

Fig.2 shows an automatic transmission regulating system; and l i Fig. 3 shows an automatic switching system employing the invention.

Referring to Fig. 1, a series of vacuum tubes V1, V2 and V; are coupled in cascade arrangement by coupling circuits each including an inductance coil L and a condenser C. The inductance L and condenser C form a tuned circuit and the values of inductance and capacity are chosen so that theresonant frequency of the circuit is relativelyhigh. The resonance frequency of each coupling circuitshould be high relatively to the frequency of the impressed signals. Each of the coupling circuits may be tuned to the same frequency or the frequencies may be different in which case the second'tuned circuit should preferably have the, higher resonance frequency. Each of the tubes is provided with a grid biasing potential by means of a battery I0, sufiicient to entirely block the space discharge through the tube in the absence of any alternating current input. Tube V1 is provided with additional negative biasing battery H connected in the same polarity as battery It]. Thetube V2 also has an additional polarizing battery [2 of the same polarity as the battery l0. A'source of space current I3 is connected to the anodes of the tubes V1, V2 and V3 respectively through the coils L, L and a, resistance R1. .The anode of tube V1 is coupled to the grid of the tube V2 by a coupling condenser l4 and a grid leak is provided through a resistance 15. The plate circuit of the tube'Vz is coupled to the grid circuit of the tube'Ys by a similar condenser l4 and grid leak I 5. A condenser 16 forms a lay-path for alternating currents in the output circuit of the tube Va. A relay R'is connected in series with the anode of the tube V3 and the resistance R1. The transformer T, having the terminals H and I8, is an input device for the cascade arrangement of tubes V1, V2, V3."

In the operation of the system shown in Fig. 1 an alternating current is impressed upon the terminals l1 and 18 from any suitable source. The system will give no response to the impressed alternating current unless the induced electromotive force in the secondary winding of the transformer T is greater than the combined voltage of the biasing batteries [0 and l I. When the impressed current is suflicient to overcome the biasing potential, the positive tips of the wave of induced electromotive force are effective to cause space discharges in the tube V1. These discharges will be in the form of impulses or trains of impulses. The effect in the output circuit of the tube V1 is toexcite high frequency oscillations in the circuit LG by impulse excitation. Between the successive impulses, the tube V1 is blocked and therefore cannot then extract energy from the operating circuit LC. The tuned circuit itself is, as usual, only slightly damped and the oscillations tend to be sustained during the period between impulses. Extended peak voltages generated in the tuned circuit LC will cause the grid of the tube V: to become positive at times, particularly during or immediately following each and to limit the output of the tube V2.

exciting impulse. The grid filament impedance of the tube V2 is greatly reduced while the grid of that tube is positive thereby intermittently introducing a large damping effect. This intermittent damping reduces the excessive peaks of the oscillations, further tending to sustain the oscillations at a relatively constant amplitude as long as the impulses continue to be applied. When the end of a train of impulses is reached, the oscillations of the circuit LC are quickly damped out in the usual manner.

The tube V2 is blocked by the polarizing batteries l0 and I2 and will not respond to an impressed wave unless the voltage generated by the wave impressed across the resistance. l 5 is greater than the combined voltage of the batteries 19 and [2. The response of "the tube V2 to a wave which is of sufiicient intensity to overcome the biasing potentials will be in the form of a train.

moreor less sustained amplitude will be gen-.

erated.

When the. alternating voltage applied to the input circuit of the tube V: is sumciently great to drive the grid. potential positive and cause a ficw of grid current in the tube,v any further in crease in the applied voltage is accompanied by an increase in the grid current andan increased fall of potential in the grid leak [5. This fall of potential isin the requisite direction to establish a. negative biasing potential upon the grid. This tends to prevent any further increase in the alternating voltage applied to the grid The volume limiting effect is a. further factor'in main: taining a substantially constant amplitude of oscillation throughout the duration of the application of impulses to the tube V1.

The final stage employing the tube V3 is an output or power stage and is biased only sufficiently to prevent a discharge when no alternating current is applied to the input circuit of the tube. The direct current component of the output current of the tube Va is delivered to the relay R. The sustained form of the train of oscillations applied to the tube V3 is adapted to give a maximum rectified current in the tube Va. The advantage of the sustained wave will readily be evident when it is considered that each cycle of the wave contributes to the rectified current and that the cycles occur in rapid succession when the circuits LC are tuned to a highfrequency. The original impulses which cause the discharge in the tubes V1 are of relatively small amplitude and low frequency and are unsuitedto the production of large rectified currents. I

The application of a sufllciently large current at terminals l1 and I8 causes the relay R to operate. Further increase in the input current beyond' the value required to operate the relay has the efiect of producing an increased fall of potential in the resistance R1 in series with the relay R. This fall of potential is in. the direction necessary to oppose the potential of the battery l3 thereby preventing further appreciable increase in the current through the relay R. This limitation of the direct current through the relay results in its improved operation.

A small decrease in the current through the terminals l1 and I8 below the value necessary trol purposes.

to operate the relay results in a large decrease in the current through the relay R which is sufficient to cause the relay to release. Continuous slight fluctuations in the input current are effective to cause the repeated operation and release of the relay R.

Regenerative efiect, if present in the system will not be detrimental provided it is not suflicient to cause self-sustained oscillations, and may be used in certain cases with beneficial results.

Fig. 2 illustrates an application of the invention to an automatic transmission regulating system in which the device of the invention is utilized to rapidly generate substantial currents for con- The system is shown in connection with a radio receiver having an antenna l9 connected through a coupling transformer 20 to ground 2|. The transformer 20 is arranged to feed energy into a controlled amplifier 22 connected in cascade with further stages of amplification 23, a detector 24 and a telephone receiver 25. vided for supplying a portion of the energy from the output of amplifier 23 to a circuit 26 similar to thesystem shown in Fig. 1. Instead of being adapted to operate a relay as shown in Fig. l, the last stage of the circuit 26 is arranged to control a vacuum tube rectifier 21. A filter or time constant circuit 28 is associated with the rectifier 21.

The rectified current from the rectifier 21 is directed through the resistance 29 to ground. The negative terminal of resistance 29 is connected through a conductive portion of the filter 28, a lead 30 and a resistance 3! and the secondary of the transformer 20 to the control grid of the amplifier 22. The cathode of the amplifier 22 is grounded, with the result that the potential across the resistance 29 is applied between the control grid and cathode of the amplifier 22 as a biasing potential.

p The system 26 is. further modified over the arrangement shown in Fig. 1 by the use of separate plate batteries for the respective vacuum tubes instead of the common battery l3. Also the biasing potentials applied to the successive grids in circuit 26 are multiple values of a potential E3 and are arranged in the descending order 3E ZE and Eg from the first stage to the last. Identical vacuum tubes are used in all the stages. This arrangement of the grid potentials in a descending arithmetical series has been found very satisfactory in practical use where exceedingly stable operation is desired together with a moderate but not exceedingly high rate of change in the output current for small changes in the input. In the operation of the system of Fig. 2 a small change in the alternating current output of amplifier 23 actuates the system 26 to produce a large change in the rectified current delivered by rectifier 21 through resistance 29. A correspondingly large change is produced in the potential across the resistance 29 and consequently a large change is efiected in the biasing potential on the grid of the amplifier 22. The change in the biasing potential is found to be proportional to the change in the output of amplifier 23 over an extended operating range. The connections are such that the bias becomes more negative when the output increases and less negative when the output decreases and thus there is effected a powerful control upon the gain of the amplifier'22 in the proper direction to restore the output of amplifier 23 to its former value. If the output current undergoes a change in amplitude so For control purposes a connection is pro abrupt as to be rm'deslrable, the change in the into play at higher 'levels.'

1 potential across'the-resistance 29 is delayed and smoothed out by the action of the filter 28 so that" the correction of the gain intheamplifier 22 is not objectionable. This limitation is useful in insuring that the control system will not respond to unusually suddenchanges of brief dura- Fig. 3shows another application of the invention in the form--of' a"systeinfor automatically switching from one-radio receiver to another to avoidthe'undesirable effects of fading. 'Inthissystem the device" of the invention is employed to operate a switching relay. A' main receiver 32 and a reliefreceiver-33 are arranged to be connected alternately through a"balanced-' threewindingtransformer? and a lowpass filter 35 withatelephone receiver 36L Receivers 3'2 and 33 are preferably located at points spaced several wave lengths apart so that'fadingfdoe's not-occur simultaneously in them. The=filter 35* and receiver 35 arebalanced by me'an's of the b'alancing network 31. The main-receiver 32 1s adapted to generata in' addition to-the'desired signal currents, 'a'control current ofa frequency preferably above the range of the desired signals.

' For-the purposeof switching in the relief receiver. when required, a connection is provided for impressingev portion of the energy output of re oeiver 32 upon a transformer 38 and amplifying tubes 33 and-43-connected in cascade. The amplifiers 39 and 40 are tuned for the control frequency by means of resonant circuits 4| and 42. The resonant circuit is coupled to a detecting circuit'43 very similar to the system of Fig. 1, but connected to a polarized relay 44 instead of the neutral relay R. The relay 44 has an armature 45 pivoted at the center; contacts 46 and 41,

adjacent the respective ends of the armature; a

pair of polarizing windings 50, 60 and a pair of operating windings 10, Hi. The windings G0, 60 are energized by current supplied from a polarizing battery 65. The armature 45 has a common connection to the respective output circuits of receivers 32 and 33. Contact 46 is connected to the output of receiver 32 and forms, when closed by armature 45, a short circuit across the output of receiver 32. Contact 41 is connected to the output of receiver 33'and forms, when closed by armature 45, a short circuit across the output of receiver 33.

The detecting circuit 43 comprises three vacuum tubescoupled by resonant transformers 1|, H. The tubes are supplied with space current from the common source l3 and have a filament supply batteryv 48 connected in series with resistances 49, 59 and 5|, Graded biasing potentials are available across the resistances 49, 53 and 5| upon the passage of filament current therethrough. The grid of the first tube in circuit 43 is arranged to be biased by a potential including the potential drop across the three resistances 49, and 5|. The second tube isbia-sed by the two resistances 49 and 50 and the third tube has its grid bias limited by resistance 49.

In the operation of the system'shown in Fig. 3 the control current generated by main receiver 32 is normally sufiicient, when applied to the circuit 43 by the amplifiers 39, 40 to maintain an operating current in the relay windings 19, 1|] large enough to overcome the polarizing action of the windings 60, 60 and to cause the armature 45 to beheld against contact 41. Receiver 33 is thereby normally short circuited and receiver 32 is connected through transformer 34 to the filter 35 and the telephone 36. Upona slight falling off in the output of receiver 32 there is a corresponding decrease in the control currentimpressed upon the transformer 38. This current decrease, effective through the amplifiers 39 and '40 and the circuit 43 causes a disproportionately large decrease in the current supplied to the relay windings 10, 10. The relay armature 45 is immediately reversed by the action of the windings B3, 63, opening the contact 4? and closing the contact 46 to effect'the desiredswitching operation' The result of the switching operation is to open the short circuit which is normally completed across the output of receiver 33 and to close a short circuit across the output of receiver 32. Receiver 33 isthereby connectedto the filter 35 and receiver 36 in place of the main receiver 32. Upon restoration of the output of receiver 32 to its normal value, there is anincrease in the control current resultingin' another reversal of the relay 44, restoring the circuit to normal condition.

Tuned circuits 4| and 42 serve a double purpose of increasing the eificiency of the amplifiers 39 and 40'in'the amplification of the control currents and of attenuating currents of the signal frequencies which may be impressed upon these amplifiers. The signal frequency currents, if

transmitted through to the detecting circuit 43 in any substantial amounts, tend to cause rapid reversals of relay 44'which are troublesome.

' In certain cases, the polarized relay 44 shown in Fig. 3has been foun'dpreferable to the neutral relay R of Fig. 1, giving smoother operation free from chattering.

What is claimed is:

l. A space discharge detecting system comprising a plurality of similar space discharge tubes each polarized by a potential more than sufiicient to block the space discharge in that tube, means for impressing thereon an input wave sufficient in amplitude to overcome the biasing potential in the first tube thereby releasing a space discharge therein, a plurality of tuned circuits connected to couple said tubes in cascade arrangement, and an indicating means actuated by the last tube in the series when said input wave is applied to the first tube.

2. A detecting system comprising a plurality of voltage amplifying tubes and tuned circuits connected alternately in cascade arrangement, each tube being polarized by a potential more than suificient to block the space discharge therein, but each tube after the first having less polarizing potential than the preceding tube, a power amplifying tube connected to the output of said cascade arrangement of tubes and circuits, said power tube being polarized by a potential just suflicient to block the space discharge therein, and an indicating device connected in the output of said power tube.

3. A wave detector comprising a plurality of similar space discharge devices, a plurality of tuned circuits coupling said space discharge devices in cascade arrangement, the last of said space discharge devices in the series being polarized by a potential just sufiicient to block the space discharge therein and the preceding discharge devices being blocked by successively increasing potentials. I

4. A wave detector comprising a plurality of three-electrode space discharge devices, a plurality of resonant circuits coupling said space discharge devices in cascade arrangement, a space current source connected to the anode of each. of said discharge devices, and means for impressing polarizing potentials on the control electrodes of said devices, the polarizing potential of the last discharge device of the series being just suflicient to block the space discharge therein and the polarizing potentials of the preceding discharge devices in the series increasing successively towards the first device of the series.

5. A wave detector in accordance with claim 4 in which the polarizing potentials of the discharge devices have magnitudes respectively in accordance with the. arithmetic series .1, 2, 3-counting from the last discharge device of the series.

6. A system for discriminating between alternating current waves of slightly different amplitudes comprising a pluralityof amplifying space discharge devices, the last of said devices being polarized by a potential just sufilcient to block the spacedischargetherein andthe preceding discharge devices being blocked by potentials successively increasing toward the first device of the series and indicating means connected with the last device of the series. r

7. A wavedetecting system comprising. a source of waves to be detected, a pair of resonant circuits tuned to a frequency somewhat higher than the frequency of the waves from said source, means adapted to be actuated by said source to impress a train-of impulses uponone ofsaid resonant circuits, and current limiting means inserted between said resonant circuits for transmitting to the second resonant circuit oscillations of nearly constant amplitude during the impulse excitation of the first resonant circuit bysaid train of impulses.

8. In a switching system, a relay and means for actuating the same in response to a slight change in the amplitude of an alternating current wave comprising a plurality of amplifying space discharge devices, the last of said devices being polarized by apotential just sufiicient to block the space discharge therein, and the preceding discharge devices being blocked by potentials successively increasing toward the first device of the series.

4 9. The method of detecting an alternating current which comprises employing the peaks of the alternating current wave for impulse excitation of an oscillatory circuit of a natural frequency higherthan that of the said alternating current, forming said natural oscillations into a train of impulses of increased energy content with limitation of the maximum amplitude of said oscillations, employing said train of impulses to excite additional oscillatory circuits of the same natural frequency with further limitation of amplitude and increase of energy, and utilizing said oscillations to give an indication.

10. A space discharge detecting system comprising a plurality of similar space discharge devices, means forpolarizing each of said devices by a potential more than sufficient to block the space' discharge in that device, a plurality of tuned circuits coupling said devices in cascade arrangement, and an indicating means actuated by the last device in the series when an electromotive force resulting from an incoming wave is applied to the first device of the series.

RUSSELL S. OHL. 

